1844, American English, from Spanish loco (adj.) "insane," of uncertain origin, perhaps from Arabic lauqa, fem. of 'alwaq "fool, crazy person." Loco-weed (1877) was name given to species of western U.S. plants that cause cattle and horse diseases that make them stagger and act strangely.

in loco parentis

To assume the duties and responsibilities of a parent: “Because Jack's parents were out of town, his sister acted in loco parentis and punished him for staying out so late.” From Latin, meaning “in the place of a parent.”

Note: At one time, colleges and universities acted in loco parentis for their students, but this is no longer true.